VIII. NIH TOOLBOX COGNITION BATTERY (CB): COMPOSITE SCORES OF CRYSTALLIZED, FLUID, AND OVERALL COGNITION

The NIH Toolbox Cognitive Function Battery (CFB), together with test modules for motor, sensory, and emotional functioning, comprise the “NIH Toolbox for Neurological and Behavioral Function.” The development of the NIH Toolbox was commissioned by multiple NIH institutes to provide brief, efficient and highly accessible measures for broad use in future epidemiologic and clinical research. Additional important goals of the NIH Toolbox initiative were to use nonproprietary instruments that could be administered in both English and Spanish, and that would be able to tap behavioral constructs across the lifespan (ages 3 to 85 years). Chapter 1 in this monograph describes the rationale for the NIH Toolbox, a NIH Blueprint initiative. That chapter also describes the methods for identifying target subdomains and appropriate test instruments. The NIH Toolbox CFB is currently comprised of 7 test instruments that measure 8 abilities within 6 major cognitive domains. The test instruments are described in detail in Chapters 2 through 6 of this monograph: Chapter 2—the Dimensional Change Card Sort (DCCS) Test (Executive Function-Cognitive Flexibility) and the Flanker Inhibitory Control and Attention Test (Executive Function-Inhibitory Control and Sustained Attention); Chapter 3—the Picture Sequence Memory Test (Episodic Memory-Visual); Chapter 4—the Picture Vocabulary Test (Language-Vocabulary Comprehension), and the Oral Reading Recognition Test (Language-Reading Decoding); Chapter 5—the List Sorting Working Memory Test (Working Memory); and Chapter 6—the Pattern Comparison Processing Speed Test. Many researchers will want to consider measures of these various cognitive functions separately, but others are expected to focus on a smaller number of composite scores that represent overall cognition and/or certain categories of abilities. Such composite scores can be defined using factor analytic methods (see Mungas et al., this volume) but these may yield different combinations of scores for different age groups and consequently may not be well suited to longitudinal research or research that spans multiple age ranges (e.g., early childhood to adult). Another approach to defining composite scores is to group tests that may tap more than one specific ability domain but share certain theoretical and psychometric characteristics across the lifespan. In the two-component theory of intellectual development (Cattell, 1971; Horn 1968, 1970), for example, the premise is that the organization of fluid and crystallized abilities is dynamic, developing and transforming throughout the life span (Li et al., 2004). Fluid abilities are used to solve problems, think and act quickly, and encode new episodic memories, and play an important role in adapting to novel situations in everyday life. Fluid abilities are presumed to be especially influenced by biological processes and less dependent on past exposure (learning experiences). These abilities improve rapidly during childhood, typically reaching their peak in early adulthood, and then decline as adults get older. Crystallized abilities, in contrast, are presumed to be more dependent on experience, and less by biological influences. They represent accumulated store of verbal knowledge and skills, and thus are more heavily influenced by education and cultural exposure, particularly during childhood. These abilities show marked developmental change during childhood, but they typically continue to improve slightly into middle adulthood and then remain relatively stable. Age-related improvements in fluid abilities in early development are thought to support acquisition of the knowledge needed for crystallized abilities, thus accounting for stronger correlations between fluid and crystallized abilities early in life, compared with those found in later years (Cattell, 1971; Horn 1968). Once developed, crystallized abilities tend to be fairly stable throughout adulthood and much less susceptible to the effects of aging and health status during aging than is the case with fluid abilities. In contrast, fluid abilities tend to be more sensitive to neurobiological integrity, including changes in brain functioning with aging and in a variety of neurological disorders that alter brain structure and function. Here we present data from the children’s validation sample for the NIH Toolbox CFB that is based on three candidate summary scores: Toolbox Crystallized Cognition Composite, Toolbox Fluid Cognition Composite, and Toolbox Cognitive Function Composite (a combination of both crystallized and fluid scores). Results are based on 208 children, ages 3 to 15. We expected all three summary scores to increase fairly rapidly with age, in contrast to results obtained during adulthood (Weintraub et al., submitted). We also present psychometric information, such as test/retest reliability and associations with well accepted, but mostly proprietary, instruments that also putatively tap crystallized and fluid abilities (i.e., “gold standard” measures). Although we predicted that the NIH Toolbox CFB summary scores would show good convergent validity with relevant gold standard measures, we expected that there would be less evidence of discriminant validity across fluid and crystallized abilities, particularly among younger children. This hypothesis was based upon the expectation that fluid and crystallized abilities develop rapidly and roughly in parallel during early childhood, whereas they tend to diverge during adulthood with larger age effects on fluid abilities (Horn & Cattell, 1967 Sattler, 2001; Weintraub et al., submitted; WAIS-III WMS-III Technical Manual, 1997). With both children and adults it is important to evaluate the potential impact of demographic variables on various neuropsychological tests (Heaton, Taylor, & Manly, 2003). For example, information about which demographic variables are associated with performance in healthy individuals can inform important group matching decisions in future research, as well as the creation and use of standards for evaluating performance relative to norms. In addition to predicted changes with age, performance on certain measures may also differ with respect to gender, family income, and race/ethnicity. Whereas level of formal education also is a significant predictor of cognitive test performance in adulthood (e.g., Heaton et al., 2003, 2004), in children age and education are almost totally confounded. However, for children, maternal level of education also has been shown to be a significant predictor of IQ and various aspects of neuropsychological test performance. The relation of each of these demographic variables with the composite measures of NIH Toolbox CFB performance were examined. Finally, to further explore validity of the Toolbox composite measures, we examined associations between all cognitive summary scores and a few relatively gross measures of health and everyday functioning (maternal reports of health and school performance).